Senate Democratic Majority Leader Harry Reid reached out to Mayor Bloomberg today to urge him not to get behind former congressman Harold Ford Jr., if the Tennessee transplant decides to take on Sen. Kirsten Gillibrand in a primary, sources told The Post.

The conversation came the same day that Bloomberg’s 2009 campaign manager Bradley Tusk and his pollster, Doug Schoen, had lunch with Ford, sources said.

Reid placed the call after reports that Bloomberg was open to backing Ford – who’s seriously weighing a challenge to Gillibrand – against the junior senator, who was appointed to her post last year and has struggled to gain traction with voters.

The sources said Bloomberg indicated he likely won’t support Ford – and may not even get involved at all – but also made clear he has problems with Gillibrand, with whom he’s tangled over health care reform in recent weeks.

Bloomberg backed Caroline Kennedy behind the scenes for the senate post when Hillary Rodham Clinton left it to become secretary of state, and he wasn’t happy when Gov. Paterson named Gillibrand – then a second-term congresswoman.

Tusk confirmed the lunch but refused to discuss details.

A Bloomberg spokesman declined comment, and a Reid spokesman didn’t immediately respond to a request for comment.